Gaseous discharge display device with a layer of electrically resistive material

ABSTRACT

A visual display device incorporates an array of direct-current discharge devices. A block of electrically insulating material has a plurality of gas-filled cavities, each forming a discharge space for one discharge device, or a single gas-filled cavity common to all discharge devices. A plurality of transparent anode conductors on a face of a second block of electrically insulating material, sealed to the first block, and in registration with the cavities, form anode electrodes for one co-ordinate of the array. Cathode electrodes are carried by a face of a third block of electrically insulating material, also sealed to the first block, and those cathode electrodes of the other co-ordinate of the array are connected by way of electrically resistive material to one of a plurality of cathode conductors. The cathode conductors, which are isolated from the discharge space or spaces, cathode electrodes and electrically resistive material are all carried on said face of the third block.

United States Patent [191 Walters GASEOUS DISCHARGE DISPLAY DEVICE WITHA LAYER OF ELECTRICALLY RESISTIVE MATERIAL [75] Inventor:

I Frank Walters, Bury, England [73] Assignee: Ferranti Limited,Hollinwood, En-

gland [22] Filed: May 19, 1971 [21] Appl. No.: 144,872

[56] References Cited UNITED STATES PATENTS 3,603,837 9/1971 Turner..3l3/220 3,553,458 1/1971 Schagen... ..3l5/l69 R X 3,206,638 9/1965Moore ....3l5/l69 TV X 3,334,269 8/1967 L'Heureux ..315/l69 TV X [451May 22,1973

Primary Examiner-Palmer C. Demeo Attorney-Cameron, Kerkam & Sutton [5 7]ABSTRACT A visual display device incorporates an array of directcurrentdischarge devices. A block of electrically insulating material has aplurality of gas-filled cavities, each forming a discharge space for onedischarge device, or a single gas-filled cavity common to all dischargedevices. A plurality of transparent anode conductors on a face of asecond block of electrically insulating material, sealed to the firstblock, and in registration with the cavities, form anode electrodes forone co-ordinate of the array. Cathode electrodes are carried by a faceof a third block of electrically insulating material, also sealed to thefirst block, and those cathode electrodes of the other co-ordinate ofthe array are connected by way of electrically resistive material to oneof a plurality of cathode conductors. The cathode conductors, which areisolated from the discharge space or spaces, cathode electrodes andelectrically resistive material are all carried on said face of thethird block.

28 Claims, 7 Drawing Figures Patented May 22, 1973 3,735,183

2 Sheets-Sheet 1 5 19 F164. 75 vi? GASEOUS DISCHARGE DISPLAY DEVICE WITHA LAYER OF ELECTRICALLY RESISTIVE MATERIAL THIS INVENTION relates tovisual display devices, and in particular to such devices comprising anarray of gas-filled direct-current cold-cathode dischai' ge devices eachof which may be struck or extinguished to produce a display of therequired form.

Visual display devices are known which incorporate an array ofdirect-current discharge devices formed by one or more gas-filledcavities in a block of an electrically insulating material such as glassor ceramic. A set of conductors is formed on a furtherblock which isthen sealed to the first block so that the conductors form one electrodeof each discharge device. Each discharge device is also provided with asecond electrode carried by a face of a third block, also sealed to thefirst block, and a series impedance connected between that secondelectrode and one of a second set of conductors.

It has usually been necessary to arrange the series impedances and thesecond set of conductors outside the display device, though copendingapplication Ser. No. 869,799 now issued as US. Pat. No. 3,603,837assigned to the assignee of the present invention describes and claims adisplay device with integral load resistors in which the two sets ofconductors may be produced in the same manner.

It is an object of the invention to provide a visual display device ofthe type described in which the load impedances are formed in a simplemanner within the display device.

According to present inventions a visual display device incorporating anarray of direct current discharge devices comprises a first block ofelectrically insulating material having one or more gas filled dischargespaces, a second block of electrically insulating material sealed to thefirst block, a set of electrical conductors on the second block, eachconductor forming a first electrode of at least one of said dischargedevices a third block of electrically insulating material sealed to thefirst block and a plurality of second electrodes, one for each of saiddischarge devices, carried by a face of the third block adjacent to thedischarge space or spaces, at least one set of further electricalconductors formed on said face of the third block and electricallyisolated from each discharge space, and a layer of electricallyresistive material carried by said face of the third block andconnecting each second electrode to a selected one of the, or each, setof further conductors.

The second electrodes, further conductors and electrically resistivematerial may all be formed on the surface of the third block. V

The discharge spaces in the first block may comprise a plurality ofcavities arranged in a two co -ordinate array and each conductor on thesecond block may form an electrode for each cavity associated with oneco-ordinate of the array, each one of the, or each, set of furtherconductors being connected to the second electrodes associated with thecavities of the other coordinates of the array.

The invention will now be described with reference to the accompanyingdrawings, in which:

FIG. I is a sectional side view of a display device according to a firstembodiment of the invention;

FIG. 2 is an enlarged 'view of part of FIG. I;

FIG. 3 is a sectional side view of a display device according to asecond embodiment;

FIGS. 4, 5 and 6 are enlarged views of parts of three furtherembodiments; and

FIG. 7 is an enlarged sectionalview of a further embodiment.

The display device shown in FIGS. 1 and 2 is made in three parts. Thecenter spacer 10 is a block of glass or similar material having formedin it a matrix of small cavities 11. These cavities may, for example, beof circular or square cross-section, and are preferably arranged in therows and columns of a rectangular matrix. The upper block 12, of asimilar material to spacer 10, carries on its underside a number ofparallel transparent evaporated anode conductors 13, say of stannicoxide, only one of which is shown in FIG. 1. Each anode conductor 13passes across the top of all the cavities 11 in one row of'the array,which is intended to be viewed from the top as shown in the FIG. 1.

The lower block 14, also of a similar material to spacer l0, carries'thecathode electrodes 15, load resistors l6 and cathode conductors 17 forthe entire matrix of discharge tubes. Each discharge tube has anindividual cathode electrode 15 and individual load resistor 16. Thecathode conductors 17 comprise a number of parallel strips similar toanode conductors 13, each strip interconnecting the load resistors 16associated with a particular column of the matrix. The cathodeconductors are spaced from the electrodes of adjacent columns by an airgap or by an insulating material. The complete display device thereforecomprises a plurality of discharge cells defined by the cavities 11 inthe block 10, the cavities being filled with a suitable gas and closedby the covers 12 and 14. The joints between the various blocks aresealed with a suitable material and provide a gas seal for the device.

The formation of the cathode electrodes 15, load resistors l6 andcathode conductors 17 on the lower cover plate 14 requires a number ofoperations, and the various components may be made from a number ofalternative materials. The load resistors 16 are formed first, by ascreen printing process, and are arranged in the appropriate positionson the lower cover plate 14. The resistive material may, for example, beruthenium dioxide or thallium oxide. The ruthenium oxide requires to befired at about 650 C, whilst the thallium oxide may be fired at about500 C. Either the cathode conductors or the electrodes may be formednext. The cathode conductors 17 need not be transparent, and may beformed by evaporating through a mask a layer of chromium with a coveringof gold. Finally, the cathode electrodes are formed by a similarprocess, and may be formed at the same time as the conductors if thesame materials are used. 7

Each cell of the display device may be caused to conduct by applying adc. potential between the anode conductor 13 and cathode conductor 17which together uniquely define the desired cell. A display may be builtup by causing a number of cells to conduct simultaneously.

The resulting display device has the form shown in FIG. 1. However, itis not essential to use a spacer block 10 as shown, and this may bereplaced by a builtup layer 18 of glass formed by screen printing. Thelatter arrangement results in a device as shown in FIG. 3, in which thewalls 18 defining each individual cell are formed by one or more screenprinting operations 3 using a suitable glass. This is used in paste formand subsequently fired. The glass walls 18 cover the load resistors 16and the cathode conductors 17, leaving exposed only the cathodeelectrodes 15. The cavities produced have inclined walls due to thebuild-up of successive layers of the walls 18.

Alternatively, the spacer formation defining individual cells may beomitted altogether, though a spacer is necessary around the edge of thedisplay device. However, if this is done the cathode conductors must becovered with an insulating material to prevent discharges taking placeother than in the required positions.

FIG. 4 illustrates such an arrangement, where each individual loadresistor 16 and all the cathode conductors 17 on the block 14 arecovered by an insulating layer of glass 19 formed by screen printing andfiring a suitable paste. The anode conductors are formed as describedpreviously on the block 13. Only the cathode electrode 15 of each cellon the block 14 is exposed, and thus the discharges will take placebetween these electrode and the appropriate row or anode conductors 13.

As before there is a choice of materials for the conductors, electrodesand resistors, though the materials referred to above are particularlysuitable.

Using the constructions referred to above it is possible to provide amatrix of discharge tubes with the individual cells spaced about 0.03inches apart. This spacing is determined to a certain extent by theresistance of the material used to form the load resistors. If a closerspacing of individual cells is required then a construction such as thatshown in FIG. may be used. In this arrangement the cathode electrode andpossibly part of the load resistor of one cell overlaps the resistor andcathode conductor of another, being insulated from it by a layer ofglass.

As will be seen from FIG. 5 only the cathode conductors 17 are actuallyformed on the surface of the block 14. The cathode electrodes are formedon top of a layer 19 of insulating glass which covers each cathodeconductor and its associated load resistors. It will be seen from acomparison of FIGS. 4 and 5 that the cathode electrodes may be arrangedmuch closer together using the arrangement of FIG. 5 than was possiblewith the earlier arrangements.

Although in the embodiments described above the resistive material isinsulated from the discharge space, this is in fact not essential, owingto the high resistivity of the material. However, it is essential thatthe cathode conductors be separated from the discharge space. Hence thesimple arrangement of FIG. 6 may be used. In this arrangement, thecathode conductors 17 are formed on the surface of the block 14 and thena complete layer 16 of resistive material is formed. The cathodeelectrodes 15 are then formed on the surface of the resistive layer. Dueto the high resistivity of the material forming the layer 16, only therequired cell will conduct owing to the greater distances between aselected cathode conductor and the cathode electrodes associated withanother cathode conductor. Hence there will be no risk of the wrongcells conducting.

In a further embodiment, shown in FIG. 7, the lower block 14 carries thecathode electrodes, and a plurality of load resistors and cathodeconductors for each discharge cell of the matrix. The resistors arebuilt up in a stack, with insulating material supporting and isolatingthe various layers. As shown in FIG. 7, three sets of cathode conductorsare formed, the three conductors shown being denoted by the references17a, 17b and 17c respectively. A first layer 16a of resistive materialis formed on the surface of the block 14 with one end of the layer inelectrical contact with one of the cathode conductors 17a. Alongside theresistive layer is formed an insulating layer 1911. This insulatinglayer supports a second layer 16b of resistive material which isconnected to a second conductor 17b at one end and which overlaps thefirst resistive layer 16a at the other end. The remainder of theresistive layer 16a and the conductor 17a are covered by a second layerof insulating material. A third layer of resistive material 16c isformed over the insulating layer 19b, overlapping layer 16b at oneendand making contact with conductor 170 at the other end. The remainderof resistive layer 16b is covered with an insulating layer 20.

Each cell of the display device thus has one anode connection and threepossible cathode connections, any one cell being caused to conduct byapplying a suitable d.c potential between the anode conductor 13 and aselected one of the cathode conductors 17 which together uniquely definethe desired cell.

The intensity of the discharge within the cell depends upon the cathodeconductor which is selected. If conductor 170 is used, this is connectedthrough a single resistive layer to the cathode electrode 15, giving adischarge of the maximum intensity. Cathode conductor 17b, however, isconnected to the cathode electrode through resistive layer 16b in serieswith part of layer 16c. Hence the total resistance is greater and thedischarge current will be lower, giving a discharge of lower intensity.Similarly, the use of cathode conductor 17a causes the total seriesresistance to be that of layer 160 plus part of each of layers 16b and16c. This gives the maximum series resistance and hence the lowestintensity discharge. This arrangement may be used with only two, or withmore than three, resistive layers and sets of cathode conductors.

Other forms of construction are also possible, so long as they satisfythe requirement that the load resistors are supported by the surfacewhich carries the associated cathode conductors. For example, a spaceras shown at 10 on FIG. 1 may be used with constructions of FIGS. 4, 5and 6, with the spacer separated from the lower cover plate 14' with itsresistors and electrodes. The spacer 10 then serves to locate thedischarge of each cell in a precise position.

The anode conductors 13 need not be transparent, so long as they arethin enough to avoid seriously obscuring the discharge.

Although in the above embodiments the series resistors have beenconnected to the cathode electrode of each cell, the resistors mayalternatively be connected on the anode side of the circuit.

What we claim is:

1. A visual display device incorporating an array of direct-currentdischarge devices comprising a first block of electrically insulatingmaterial having one or more gas filled discharge spaces, a second blockof electrically insulating material sealed to the first block, a set ofelectrical conductors on the face of the second block adjacent the spaceor spaces, each conductor forming a first electrode of at least one ofsaid discharge devices, a third block of electrically insulatingmaterial sealed to the first block and a plurality of second electrodes,one for each of said discharge devices, carried by a face of the thirdblock adjacent the discharge space or spaces, at least one set offurther electrical conductors on said face of the third block andelectrically isolated from each discharge space, a layer of electricallyresistive material, carried by said face of the third block andconnecting each second electrode to a selected one of the, or each, setof further conductors and a layer of insulating material covering theface of the third block, except in the vicinity of the secondelectrodes, and the resistive material and each further conductor on thesurface of the third block.

2. A visual display device as claimed in claim 1 in which each secondelectrode is stacked over a further conductor associated with anadjacent second electrode.

3. A visual display device as claimed in claim 1 in which the layers ofelectrically resistive material connecting each second electrode to onefurther conductor of each of a plurality of sets are stacked one abovethe other and are separated by electrically insulating material.

4. A visual display device as claimed in claim 1 in which the dischargespaces in the first block comprise a plurality of cavities arranged in atwo co-ordinate array.

5. A visual display device as claimed in claim 4 in which each conductoron the second block forms an electrode for each cavity associated withone coordinate of the array and each one of the, or each set of, furtherconductors is connected to the second electrodes associated with thecavities of the other coordinate of the array.

6. A visual display device as claimed in claim 1 in which the first,second and third blocks are of the same electrically insulatingmaterial.

7. A visual display device as claimed in claim 6 in which theelectrically insulating material is glass.

8. A visual display device as claimed in claim 1 in which theelectrically resistive material is thallium oxide.

9. A visual display device as claimed in claim 1 in which theelectrically resistive material is ruthenium dioxide.

10. A visual display device as claimed in claim 1 in which theconductors on the second block are transparent.

11. A visual display device as claimed in claim 10 in which thetransparent conductors are of stannic oxide.

12. A visual display device as claimed in claim 1 in which the furtherconductors are of chromium plated with gold.

13. A visual display device incorporating an array of direct-currentdischarge devices comprising one or more gas filled discharge spacesformed between a first and a second block of electrically insulatingmaterial, a set of electrical conductors on the face of the first blockadjacent the discharge space or spaces, each conductor forming a firstelectrode of at least one of said discharge devices, means for sealingsaid second block of electrically insulating material to the firstblock, a plurality of second electrodes, one for each of said dischargedevices, carried by a face of the second block adjacent the dischargespace or spaces, at least one set of further electrical conductors onsaid face of the second block, said further electrical conductors beingelectrically isolated from each discharge space, a layer of electricallyresistive material, carried by said face of the second block andconnecting each second electrode to a selected one of the, or each, setof further conductors and a layer of insulating material covering theresistive material and each further conductor on the surface of thesecond block.

14. A visual display device as claimed in claim 13 in which the secondelectrodes, further conductors and electrically resistive material areall formed on the surface of the second block, said layer of insulatingmaterial extending to said face of said second block between each saidsecond electrodes and the adjacent one of the, or each, set of furtherconductors.

15. A visual display device as claimed in claim 13 including spacermeans between said first and said second block defining said dischargespaces.

16. A visual display device as set forth in claim 15 wherein said spacermeans comprise built up insulative wall sections covering theelectrically resistive material and each further section.

17. A visual display device as set forth in claim 15 wherein saiddischarge spaces have inclined walls forming spaces of increasingcross-section extending from the second block to the first block.

18. A visual display device as claimed in claim 13 in which each secondelectrode is stacked over a further conductor associated with anadjacent second electrode.

19. A visual display device as claimed in claim 13 in which the layersof electrically resistive material connecting each second electrode toone further conductor of each of a plurality of sets are stacked oneabove the other and are separated by electrically insulating material.

20. A visual display device as claimed in claim 13 in which thedischarge comprising a plurality of cavities arranged in a twoco-ordinate array.

21. A visual display device as claimed in claim 19 in which eachconductor on the first block forms an electrode for each cavityassociated with one co-ordinate of the array and each one of the, oreach set of, further conductors is connected to the second electrodesassociated with the cavities of the other co-ordinate of the array.

22. A visual display device as claimed in claim 13 in which the firstand second blocks are of the same electrically insulating material andin which the second electrodes, further conductors and electricallyresistive material are all formed on the surface of the second block,said layer of insulating material extending to said face of said secondblock between each said second electrodes and the adjacent one of the,or each, set of further conductors.

23. A visual display device as claimed in claim 22 in which theelectrically insulating material is glass.

24. A visual display device as claimed in claim 13 in which theelectrically resistive material is thallium oxide.

25. A visual display device as claimed in claim 13 in which theelectrically resistive material is ruthenium dioxide.

26. A visual display device as claimed in claim 13 in which theconductors on the second block are transparent.

27. A visual display device as claimed in claim 26 in which thetransparent conductors are of stannic oxide.

28. A visual display device as claimed in claim 13 in which the furtherconductors are of chromium plated with gold.

2. A visual display device as claimed in claim 1 in which each secondelectrode is stacked over a further conductor associated with anadjacent second electrode.
 3. A visual display device as claimed inclaim 1 in which the layers of electrically resistive materialconnecting each second electrode to one further conductor of each of aplurality of sets are stacked one above the other and are separated byelectrically insulating material.
 4. A visual display device as claimedin claim 1 in which the discharge spaces in the first block comprise aplurality of cavities arranged in a two co-ordinate array.
 5. A visualdisplay device as claimed in claim 4 in which each conductor on thesecond block forms an electrode for each cavity associated with oneco-ordinate of the array and each one of the, or each set of, furtherconductors is connected to the second electrodes associated with thecavities of the other co-ordinate of the array.
 6. A visual displaydevice as claimed in claim 1 in which the first, second and third blocksare of the same electrically insulating material.
 7. A visual displaydevice as claimed in claim 6 in which the electrically insulatingmaterial is glass.
 8. A visual display device as claimed in claim 1 inwhich the electrically resistive material is thallium oxide.
 9. A visualdisplay device as claimed in claim 1 in which the electrically resistivematerial is ruthenium dioxide.
 10. A visual display device as claimed inclaim 1 in which the conductors on the second block are transparent. 11.A visual display device as claimed in claim 10 in which the transparentconductors are of stannic oxide.
 12. A visual display device as claimedin claim 1 in which the further conductors are of chromium plated withgold.
 13. A visual display device incorporating an array ofdirect-current discharge devices comprising one or more gas filleddischarge spaces formed between a first and a second block ofelectrically insulating material, a set of electrical conductors on theface of the first block adjacent the discharge space or spaces, eachconductor forming a first electrode of at least one of said dischargedevices, means for sealing said second block of electrically insulatingmaterial to the first block, a plurality of second electrodes, one foreach of said discharge devices, carried by a face of the second blockadjacent the discharge space or spaces, at least one set of furtherelectrical conductors on said face of the second block, said furtherelectrical conductors being electrically isolated from each dischargespace, a layer of electrically resistive material, carried by said faceof the second block and connecting each second electrode to a selectedone of the, or each, set of further conductors and a layer of insulatingmaterial covering the resistive material and each further conductor onthe surface of the second block.
 14. A visual display device as claimedin claim 13 in which the second electrodes, further conductors andelectrically resistive material are all formed on the surface of thesecond block, said layer of insulating material extending to said faceof said second block between each said second electrodes and theadjacent one of the, or each, set of further conductors.
 15. A visualdisplay device as claimed in claim 13 including spacer means betweensaid first and said second block defining said discharge spaces.
 16. Avisual display device as set forth in claim 15 wherein said spacer meanscomprise built up insulative wall sections covering the electricallyresistive material and each further section.
 17. A visual display deviceas set forth in claim 15 wherein said discharge spaces have inclinedwalls forming spaces of increasing cross-section extending from thesecond block to the first block.
 18. A visual display device as claimedin claim 13 in which each second electrode is stacked over a furtherconductor associated with an adjacent second electrode.
 19. A visualdisplay device as claimed in claim 13 in which the layers ofelectrically resistive material connecting each second electrode to onefurther conductor of each of a plurality of sets are stacked one abovethe other and are separated by electrically insulating material.
 20. Avisual display device as claimed in claim 13 in which the dischargecomprising a plurality of cavities arranged in a two co-ordinate array.21. A visual display device as claimed in claim 19 in which eachconductor on the first block forms an electrode for each cavityassociated with one co-ordinate of the array and each one of the, oreach set of, further conductors is connected to the second electrodesassociated with the cavities of the other co-ordinate of the array. 22.A visual display device as claimed in claim 13 in which the first andsecond blocks are of the same electrically insulating material and inwhich the second electrodes, further conductors and electricallyresistive material are all formed on the surface of the second block,said layer of insulating material extending to said face of said secondblock between each said second electrodes and the adjacent one of the,or each, set of further conductors.
 23. A visual display device asclaimed in claim 22 in which the electrically insulating material isglass.
 24. A visual display device as claimed in claim 13 in which theelectrically resistive material is thallium oxide.
 25. A visual displaydevice as claimed in claim 13 in which the electrically resistivematerial is ruthenium dioxide.
 26. A visual display device as claimed inclaim 13 in which the conductors on the second block are transparent.27. A visual display device as claimed in claim 26 in which thetransparent conductors are of stannic oxide.
 28. A visual display deviceas claimed in claim 13 in which the further conductors are of chromiumplated with gold.